Loss of my paperwork and bad service and rudeness

I went into the MTN Store in Oakfields in Northmead, Benoni to change the contract from my Mother's name M.K. Lumley into my own personal name N.D. Lumley all paperwork was completed in Rica documentation and a signature of authority to change account holder was given from my mother and Rica documentation was provided from myself and my mother. Lisa***ner of Oakfields) and Mpho( Employee of the store) lost all the paperwork. MTN has also changed my cell phone contract from contract asked to Pre-paid without me or my mother authorising it) and now I have to buy Airtime which is really inconvenient. No-one is getting back to me about this. I handed all the paperwork in 2 weeks ago and the whole nightmare of upgrading started as early as the 8th May then I had a problem with MTN changing my contract from contract to pre-paid without my consent and now they have lost my paperwork to change the cell phone account to my name. I would appreciate it if MTN could sort this out immediately and come back to me.